1. Field of the Invention
The invention concerns a method for the plasma treatment of workpieces, wherein the workpiece is inserted in a plasma chamber of a treatment station, which can be at least partially evacuated, and wherein the workpiece is positioned inside the treatment station by a mounting element.
The invention also concerns a device for the plasma treatment of workpieces, which has at least one plasma chamber, which can be evacuated, for holding the workpieces, in which the plasma chamber is located in the area of a treatment station, and in which the plasma chamber is bounded by a chamber floor, a chamber lid, and a lateral chamber wall and has at least one mounting element for positioning the workpiece.
2. Description of the Related Art
Processes and devices of this type are used, for example, to apply surface coatings to plastics. In particular, processes and devices of this type are also already known for coating inner or outer surfaces of containers used for holding liquids. Devices for plasma sterilization are also well known.
PCT-WO 95/22413 describes a plasma chamber for coating the inner surface of PET bottles. The bottles to be coated are raised into a plasma chamber by a movable base and connected at their mouths to an adapter. The inside of the bottles can be evacuated through the adapter. A hollow lance for supplying process gas is also inserted into the inside of the bottles through the adapter. Microwaves are used to ignite the plasma.
The same publication also describes the arrangement of a plurality of plasma chambers on a rotating wheel. This helps achieve a high production rate of bottles per unit time.
EP-OS 10 10 773 describes a feeding device for evacuating the inside of a bottle and supplying it with process gas. PCT-WO 01/31680 describes a plasma chamber into which the bottles are introduced by a movable lid that has first been connected with the mouths of the bottles.
PCT-WO 00/58631 also already describes the arrangement of plasma stations on a rotating wheel and the assignment of groups of vacuum pumps and plasma stations for an arrangement of this type to help provide favorable evacuation of the chambers and the interiors of the bottles. It also mentions the coating of several containers in a common plasma station or a common cavity.
Another system for coating the inside surfaces of bottles is described in PCT-WO 99/17334. This document describes especially an arrangement of a microwave generator above the plasma chamber and means for evacuating the plasma chamber and supplying it with operating agents through the floor of the plasma chamber.
In most of the previously known methods, silicon oxide coatings, which have the general chemical formula SiOx and are produced by the plasma, are used to improve the barrier properties of the thermoplastic material. In addition, barrier layers produced in this way can also contain carbon, hydrogen, and nitrogen components. Barrier layers of this type prevent oxygen from penetrating the bottled liquids and prevent the escape of carbon dioxide from liquids that contain CO2.
The previously known methods and devices are still not sufficiently suitable for use in a mass-production process, in which it is necessary to achieve both a low coating cost per workpiece and a high production rate.